NEC 240.67 Arc Energy Reduction...© 2020 Eaton. All rights reserved.. 7 240.67 Arc Energy Reduction...

© 2020 Eaton. All rights reserved..

NEC 240.67 Arc Energy Reduction

2© 2020 Eaton. All rights reserved..

Arc Energy Reduction - Agenda

• History of requirements

• Required documentation

• Determining if arc energy reduction is needed

• Approved methods of arc energy reduction

• Performance testing of arc energy reduction

protection systems

© 2020 Eaton. All rights reserved.. 3

History


Arc Energy Reduction - History

• Began with concern for delayed tripping of circuit breakers and NEC 240.87

• 2011 - CBs without instantaneous trip (power circuit breakers) with three options: zone selective interlocking, differential relaying or energy-reducing maintenance switching with local status indicator

• 2014 – All 1200A or larger circuit breakers (power and molded case circuit breakers) and added energy-reducing active arc flash mitigation system and approved equivalent means

• 2017 – Added use of instantaneous trip/override setting that is less than the available arcing current (and information notes) as another method to address arc energy reduction


Arc Energy Reduction - History

• Moved to fuse technology in the 2017 NEC with addition of NEC 240.67

• An effective date (1/1/2020) was established to give manufacturers an opportunity to create product

• Additional changes in NEC 2020 (in both 240.67 and 240.87)

• Note – applies NOW for jurisdictions that have adopted the 2017 NEC


Documentation


240.67 Arc Energy Reduction

240.67 Arc Energy Reduction.

Where fuses rated 1200 A or higher are installed, 240.67(A) and (B) shall apply. This requirement shall become effective January 1, 2020.

(A) Documentation.

Documentation shall be available to those authorized to design, install, operate, or inspect the installation as to the location of the fuses.

Documentation shall also be provided to demonstrate that the method chosen to reduce clearing time is set to operate at a value below the available arcing current.

Red underlined text indicates NEC 2020 change


Documentation

• Location

• Single-line diagrams that identify all 1200A fuses is an effective way to document the location of the fuses.

• Operation at arcing current (per NEC 2020)

• Documentation can vary based upon method used.

• Can include available fault current and arcing current calculations and time-current curves.

• Can include use of programs such as SKM, Easy Power or Manufacturer tools

• If other technology is required, consult equipment manufacturer.


Determining if arc energy

reduction is needed




Where fuses rated 1200 A or higher are installed, 240.67(A) and (B) shall apply. This requirement shall

become effective January 1, 2020.

(B) Method to Reduce Clearing Time.

A fuse shall have a clearing time of 0.07 seconds or less at the available arcing current, OR one of the

following means shall be provided and shall be set to operate at less than the available arcing current:

(1) Differential relaying

(2) Energy-reducing maintenance switching with local status indicator

(3) Energy-reducing active arc-flash mitigation system

(4) Current-limiting, electronically actuated fuses

(5) An approved equivalent means




Informational Note No. 1: An energy-reducing maintenance switch allows a worker to set a disconnect switch

to reduce the clearing time while the worker is working within an arc-flash boundary as defined in NFPA 70E-

2018, Standard for Electrical Safety in the Workplace, and then to set the disconnect switch back to a normal

setting after the potentially hazardous work is complete.

Informational Note No. 2: An energy-reducing active arc-flash mitigation system helps in reducing arcing

duration in the electrical distribution system. No change in the disconnect switch or the settings of other

devices is required during maintenance when a worker is working within an arc-flash boundary as defined in

NFPA 70E-2018, Standard for Electrical Safety in the Workplace.

Informational Note No. 3: IEEE 1584-2002, IEEE Guide for Performing Arc Flash Hazard Calculations, is one

of the available methods that provides guidance in determining arcing current.



Is arc reduction technology required?

• Not required for fuses rated below 1200A (e.g. A 1000A fuse in a 1200A switch does not have to comply)

• Not all fuses 1200A and above will have to have an arc energy reduction methods applied.

• ONLY fuse 1200A and above with a clearing time longer than 0.07 seconds at the arcing current

• Determining if arc energy reduction is required involves

• Calculate the available fault current

• Calculate the arcing current

• Consult the fuse time-current curve


Available fault current

• The NEC does not identify the method needed to calculate available fault current

• Need an accurate value of utility fault current

• Methods that could be used

• Bussmann Point-to-Point Method

• Ohmic or per unit method

• SKM, Easy Power, etc.

• Tools/Apps such as Bussmann FC2

• Next find arcing current

M

Main

FeederBranchFeeder

Panel

Internal Bus

Available Fault Current X


Arcing Current

• Based upon available fault current

• One method of estimating arcing current is by using IEEE 1584

• Latest edition is IEEE 1584-2018

• Arcing current calculation is significantly different (more complex and arcing current values) in 2018 edition

• IEEE 1584 is only applicable for fault current up to 106kA

• No method available above 106kA

Main

Panel

Internal Bus

Arcing Current X

M

FeederBranchFeeder


Resources and tools

• Bussmann series toolbox

• https://toolbox.bussmann.com/

• Available fault current calculator (FC2)

• Arc Reduction Calculator

• Many more!

https://toolbox.bussmann.com/


Time Current Curve Example

• Calculate arcing current and compare to time current curve

• Arc energy reduction not required for arcing currents equal or greater than this value

• Arc energy reduction is not required if arcing current is 11kA or higher for 1200A fuse

.07

Arcing current –

AER Not

Required

Arcing current –

AER Required

11kA


Resources: NEW Arc Energy Reduction Calculator

• https://arc.bussmann.com/ • Based on IEEE 1584-2018

https://arc.bussmann.com/


Selection Parameters

• Gap between electrodes (mm)

• 13 mm – Cable junction boxes

• 25 mm – Shallow/Deep low-voltage MCCs and

panelboards

• 32 mm – Low-voltage Switchgear

• Voltage

• The system voltage – 208V to 600V (480 as default)



• Electrical Configuration of electrodes

• VCB — Vertical conductors in a metal box/enclosure. With the original vertical electrode configuration, when an arc flash occurs in an enclosure, the arc is driven away from the source, down the electrodes, toward the bottom of the enclosure and out of the front.

• VCBB — Vertical conductors terminated in a metal box/enclosure’s insulating barrier. If vertical electrodes are terminated into an insulating barrier, research has demonstrated the arc hits the barrier, and the plasma cloud is directed more toward the enclosure opening. (results in the highest value of arcing current – default)

• HCB — Horizontal conductors in a metal box/enclosure. When the electrodes are placed horizontally, the arc plasma is directed from the electrode ends outward. (results in lowest value of arcing current)



• Fault Current (kA)

• Value between 0.5kA and 106kA

• If fault current is above 106kA, use 106kA since no

methods of arcing current calculations are available

• Fuse Ampacity Rating

• Maximum fuse ampacity of 2500A, above 2500A

arc energy reduction is required.



• Note: Arcing current is higher than previous calculation per previous edition of IEEE 1584

Per 1EEE

1584-2002

19,120 A

16,250 A

Pass

Pass



• Note: Arcing current is higher than previous calculation per previous edition of IEEE 1584

Per 1EEE

1584-2002

10,480 A

8,910 A

Fail

Fail


Approved methods of arc

energy reduction




Where fuses rated 1200 A or higher are installed, 240.67(A) and (B) shall apply. This requirement shall

become effective January 1, 2020.

(B) Method to Reduce Clearing Time.

A fuse shall have a clearing time of 0.07 seconds or less at the available arcing current, or one of the

following means shall be provided and shall be set to operate at less than the available arcing current:



(3) Energy-reducing active arc-flash mitigation system


(5) An approved equivalent means




• These are the zones (yellow) of protection offered by a differential relaying system (ST secondary)

• Fault outside zone (red) will not activate system since no difference in current going through CTs

• Requires shunt trip switch that is rated to open the arcing current

• Typically most expensive optionM

Main

FeederBranchFeeder

Service Panel

Internal Bus

Utility



• These are the zones of protection (yellow) offered by a energy-reducing maintenance switch

• This fused switch equipped with an energy reduction maintenance switch provides protection for downstream faults greater than its pickup value of current

• Requires bolted pressure switch based on power circuit breaker design with energy reducing maintenance switch

Main

Service Panel

M

FeederBranchFeeder

Internal Bus

Utility


GF protection, overcurrent protection

(long time trip settings and above 600% -

0.05 sec clearing), and maintenance mode

(ARMs - 2.5X switch rating)

Shunt trip switch

1200A Fuses

Zero sequence CTs

(change to phase/neutral CTs)

Example – Eaton shunt trip switch with AER relay



(3) Energy-reducing active arc flash mitigation system – arc flash relay and light sensor(s)

• Faults within this zone (Within the

enclosure) are cleared without an

intentional delay as long as they are

greater than the pickup point of the

arc flash relay and activation of a

light sensor)

• Fault outside zone (red) will not

activate system since there is no

activation of light sensors

• Requires shunt trip switch that is

rated to open the arcing current and

arc flash relay and associated

components or arc quenching device

M

Main

FeederBranchFeeder

Service Panel

Internal Bus

Utility


(3) Energy-reducing active arc flash mitigation system – Is limiter

• Faults within this zone (Within the

enclosure) are cleared without an

intentional delay as long as they are

greater than the pickup point of the Is

Limiter

• Fault outside zone (red) will not activate

system since it is ahead of the arc flash

mitigation system

• Operates only based on current (not light

sensors) and can be remotely disabled

• Requires replacement of parts after

operation (interrupter and CL fuse)

M

Main

FeederBranchFeeder

Service Panel

Utility

Is Limiter



• Faults within this zone are cleared without an intentional delay as long as they are greater than the pickup point of the relay that triggers the opening of the fuse

• Present technology finds this fuse on the MV side of the transformer

• The electronically actuated fuse would be designed to operate under lower values of currents or activated via a relay

• Commercially available units operate based on electronically preselected trip curve not based upon CT and selected trip point on relay to trigger opening fuse.

M

Main

FeederBranchFeeder

Service Panel

Internal Bus



• Definition: NEC Article 100

• Electronically Actuated Fuse. An overcurrent protective device that generally consists of a control module that provides current sensing, electronically derived time–current characteristics, energy to initiate tripping, and an interrupting module that interrupts current when an overcurrent occurs. Electronically actuated fuses may or may not operate in a current-limiting fashion, depending on the type of control selected. (CMP-10)

• Permitted method per 2020 NEC


Performance testing of arc

energy reduction protection

systems




Where fuses rated 1200 A or higher are installed, 240.67(A) and (B) shall apply. This requirement shall become

effective January 1, 2020.

(C) Performance Testing.

Where a method to reduce clearing time is required in 240.67(B), theThe arc energy reduction protection system

shall be performance tested by primary current injection testing or another approved method when first installed on

site. This testing shall be conducted by a qualified person(s) in accordance with the manufacturer’s instructions.

Performance testing of an instantaneous element of the protective device shall be conducted by a qualified

person(s) using a test process of primary current injection and the manufacturer’s recommended test procedures.

A written record of this testing shall be made and shall be available to the authority having jurisdiction.

Informational Note: Some energy reduction protection systems cannot be tested using a test process of primary

current injection due to either the protection method being damaged such as with the use of fuse technology or

because current is not the primary method of arc detection.

NEW for NEC 2020 - red text indicates TIA change


Performance Testing

• Similar requirements to NEC 230.95 GFPE

• Manufacturer instructions are very important because some arc reduction technologies are destructive to the technology themselves.

• Documentation of performance testing is required and important for the AHJ and the customer for future reference beyond initial installation.

• Primary current injection is not required where it could damage the arc energy reduction method used such as fuses and arc quenching devices

• Only qualified individuals who understand the technologies employed should perform testing.


Performance testing – Critical components

• CT’s – all solutions will employ CTs polarity of which must be checked (External / Internal)

• Electronics – ensure electronics are functioning

• Sensors – some technologies may include other types of sensors, communication with those sensors must be checked

• Test system to assure proper installation and connections per manufacturer’s instructions


CT testing

• Ratio test (tests via current or voltage to confirm CT ratio)

• Polarity test (direction of current)

• Excitation (Saturation) test (point where current can no longer be provided at the CT ratio)

• Insulation resistance test (dielectric test of CT)

• Winding resistance test (tests accuracy of CT)

• Burden test (verify that CT is supplying current that does not exceed its burden rating)

• Verify relay class (% accuracy, CT class, maximum burden) for application


Primary current injection testing

• Primary current injection testing of a fusible switch is

possible to perform (at low current levels) to test CT

polarity and electronics.

• Test equipment exists that may already be used for

GFPE testing

• Always follow test equipment manufacturer instructions

to conduct testing


Documentation

• A complete record of tests should be documented

• All tools and manufacturer documents should also

be included

• Time, date, and signed

• Professional should be qualified and experienced

with the specific manufacturer equipment

NEC 240.67 Arc Energy Reduction...© 2020 Eaton. All rights reserved.. 7 240.67 Arc Energy Reduction...

Documents

Transcript of NEC 240.67 Arc Energy Reduction...© 2020 Eaton. All rights reserved.. 7 240.67 Arc Energy Reduction...